Add ability to skip validation on postgres FK creation #244
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Validation on FK constraints in postgres can cause large tables to stay locked for a relatively long time because it has to check all rows for valid data, while also preventing new entries. Postgres implemented a way to not validate the constraint immediately so the FK can be immediately inserted, improving concurrency, with the intention that a `VALIDATE CONSTRAINT` query will be following. The validation query uses a less expensive lock, because it only needs to check rows that existed before the constraint. This allows safer migrations, and also allows for users to clean up known violations while still enforcing the constraint for new entries. This commit implements the ability to skip validation, but it does not implement the validation query.
josevalim
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Jul 5, 2020
Co-authored-by: José Valim <[email protected]>
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Two minor comments added for consistency. You will have to update the error messages after committing them though. :)
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Done! Did you want me to squash it down too? |
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💚 💙 💜 💛 ❤️ |
zachdaniel
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Validation on FK constraints in postgres can cause large tables to stay locked for a relatively long time because it has to check all rows for valid data, while also preventing new entries. Postgres implemented a way to not validate the constraint immediately so the FK can be immediately inserted, improving concurrency, with the intention that a `VALIDATE CONSTRAINT` query will be following. The validation query uses a less expensive lock, because it only needs to check rows that existed before the constraint. This allows safer migrations, and also allows for users to clean up known violations while still enforcing the constraint for new entries. This commit implements the ability to skip validation, but it does not implement the validation query.
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Validation of constraints in PostgreSQL can cause large tables to stay locked for a long time (preventing writes, because it has to check all rows in order to consider the constraint as valid. PostgreSQL has a way to get around this by first creating constraints as not valid. And then running a query to validate the constraint. The validation query does not lock the table, i.e. it can be run while allowing writes in parallel. This commit implements the ability to skip validation of constraints. It does not implement the validation query. This was inspired by elixir-ecto#244. https://www.postgresql.org/docs/current/sql-altertable.html
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…te (#271) Validation of constraints in PostgreSQL can cause large tables to stay locked for a long time (preventing writes, because it has to check all rows in order to consider the constraint as valid. PostgreSQL has a way to get around this by first creating constraints as not valid. And then running a query to validate the constraint. The validation query does not lock the table, i.e. it can be run while allowing writes in parallel. This commit implements the ability to skip validation of constraints. It does not implement the validation query. This was inspired by #244. https://www.postgresql.org/docs/current/sql-altertable.html
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Validation on FK constraints in postgres can cause large tables to stay locked for a relatively long time because it has to check all rows for valid data, while also preventing new entries.
Postgres implemented a way to not validate the constraint immediately so the FK can be immediately inserted, improving concurrency, with the intention that a
VALIDATE CONSTRAINTquery will be following.The validation query uses a less expensive lock, because it only needs to check rows that existed before the constraint. This allows safer migrations, and also allows for users to clean up known violations while still enforcing the constraint for new entries.
This commit implements the ability to skip validation, but it does not implement the validation query.
See https://www.postgresql.org/docs/12/sql-altertable.html for more details